After the visit, the six MPs headed for a private room to discuss their impressions when they said a recording device was found.

Anna Turley, MP for Redcar, said: "At the end of the meeting, we sat down to have a private conversation in a room by ourselves.

"A lady came in with some sandwiches, which was very kind. I saw her take too long to do it, she put it down and I saw her put a recording device on the floor.

"She left the room and I went over to pick up the device and there it was: a camera and a recording device for the conversation that we were having privately.

"I'm very disappointed."

A spokesman for Sports Direct declined to comment.

Ms Turley continued: "I think as a select committee, we'll get together and talk about what we did genuinely see today and there were some positive things - we think there was some effort in improvement and taking on board what the committee had said.

"But we're just very disappointed. How can we not believe that there is something to hide when everything has been so suspicious and not done with the spirit of openness?"

Iain Wright, chair of the committee, said: "I'm really disappointed in the nature and spirit in which Sports Direct have conducted this visit.

"I'm not suggesting that they were going to welcome us with open arms - we are a select committee that has been critical of working practices turning up unannounced.

"The fact that the sandwich woman who came into the room when the select committee was having a private conversation about what we had discovered... to have a recording device... I mean that's absolutely disgraceful.

"That's not the manner in which I want to conduct relations with Sports Direct. We have been critical of Mike Ashley and his company, but we want to work with him, the trade unions, with workers and others to ensure that proper, appropriate and dignified working practices are put in place.

"Why does he have that lack of trust when we have offered to work with him in an open and constructive manner?"

Mr Wright spoke to Sports Direct chief Mike Ashley on the phone after the MPs left the warehouse.

The MP said: "I don't think it was a particularly pleasant conversation for either of us."

He added: "I would have liked Mike Ashley to have been here.

"We were always going to turn up unannounced. It's what he said we could do when he came before us in June and it's what we've done now.

"I want to work with Mike Ashley in a constructive manner. I don't think he wants to work with us at all any more.

"I wanted this visit to be part of a journey of progress and improvement so that we could work together to say, 'Yep, you've really done some good stuff, well done, and this is what needs to be happening'.

"But in terms of the way it's been handled: the diversionary tactics, the secret recordings of private select committee deliberations, that is really disgusting and something I really can't agree with."

Ms Turley posted photographs of a miniature camera under a stool and next to a plate of sandwiches on Twitter.

She wrote: " Here is the camera I found which was placed under the stool on which the sandwiches were placed for our private meeting at #sportsdirect.

"Here is another pic from a colleague. This is where it was hidden & where I found it before picking it up & placing on top as previous pic."